Apparatus for moistening mixable materials

ABSTRACT

For controlling the moistening of mixable materials, particularly the moistening of foundry casting sand with water, a high-speed low-inertia auxiliary mixing tool is rotated in the sand and the quantity of water added is determined in dependence on the resistance of the sand to rotation of the tool as measured by the power consumption of an electric motor driving the tool. Since the materials used are required to be at a certain starting temperature, the temperature of the material is automatically adjusted prior to commencing the moistening operation.

I United States Patent 1 1111 3,826,476 Ahrenberg [4 July 30, 1974APPARATUS FOR MOISTENING MIXABLE 2,954,215 9/1960 Warmkcssel 259/154MATERIALS 3,109,632 11/1963 Wicgel 259/84 3,249,970 5/1966 Hartley259/154 Inventor: Kurt Ahrenberg, H Germany 3,359,766 12/1967 Haas 68/12R x h 3,379,419 4/1968 Eirich et al. 259/ [73] Assgnee' sg'z g Gustav3,414,239 12/1968 Eirich et a1. 259/104 3 many 3,497,884 3/1970 Tichy eta1. 68/12 R x [22] Filed: Mar. 7, 1973 Primary Examiner-Edward L.Roberts [2] 1 Appl' 338956 Assistant ExaminerPhilip R. Coe

Related US. Application Data Attorney, Agent, or Firm--Toren, McGeadyand [63] Continuation-impart of Ser. No. 876.461, Nov. 13. Stanger 1969,Pat. No. 3,727,894.

Foreign Application Priority Data [57] ABSTRACT Mm 19 8 a |808998 Forcontrolling the moistening of mixable materials, particularly themoistening of foundry casting sand 521 US. 01 259/154, 259/168, 259/174,with water, a high-Speed low-inertia auxiliary mixing 259/177 R tool isrotated in the sand and the quantity of water 511 1111.01. BZSC 7/04added is determined in dependence on the resistance [58] ield Of Search259/149, 154, 161, 164, of the sand to rotation of the tool as measuredby the 259 1 5 1 1 17 A, 79 15 4 power consumption of an electric motordriving the 5 04- (,3/12 73 59; 137 92; 23 1 tool. Since the materialsused are required to be at a certain starting temperature, thetemperature of the 5 References Cited material is automatically adjustedprior to commenc- UNITED STATES PATENTS ing the moistening operation.

2,904.4111 9/1959 Booth 23/188 3 Claims, 7 Drawing Figures CONTROLDEVICE PATENTEDJULBOIBH 3'.a2s.476

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This is a continuation-in-part application of my copending applicationSer. No. 876,461 filed Nov. 13, 1969 now US. Pat. No. 3,727,894 issuedApr. 17, 1973.

BACKGROUND OF THE INVENTION from the disadvantage that it is notpossible to impart a predetermined consistency to thesand, or that testsamples must frequently be taken from the sand, which interrupts thetreatment.

SUMMARY OF THE INVENTION One object of the present invention is toprovide an improved method and apparatus for controlling the moisteningof mixable materials such as foundry moulding sand.

Another object is to provide such apparatus in which the quantity ofmoistening liquid added is determined in dependence on the resistance ofthe material to an auxiliary mixing tool.

Another object is to provide such an apparatus in which the auxiliarymixing tool is a high-speed lowinertia rotary mixing tool.

Still another object is to determine the temperature of the startingmaterials for automatically adjusting the temperature to a predeterminedlevel.

According to one aspect of the present invention a method of moisteninga mixable material comprises rotating in the material a high-speedlow-inertia auxiliary mixing tool and then adding a quantity ofmoistening liquid to the material determined in dependence on theresistance of the material to the auxiliary mixing tool as measured bythe power consumption of the auxiliary mixing tool.

According to another aspect of the present invention apparatus formoistening a mixable material, comprises a container for the material, amain mixing tool for mixing the material, a high-speed low-inertiaauxiliary mixing tool, driving means to rotate the auxiliary tool in thematerial, and means to add a quantity of moistening liquid to thematerial determined in dependence on the power consumption of saiddriving means.

Preferably the auxiliary mixing tool rotates at a speed which is higherby a multiple than the main mixing tool, for example at a peripheralspeed of from to 70 me tres per second.

With the method of the invention the following advantages may beobtained.

Because the resistance of the material to a tool which rotates at highspeed is comparatively large, the power consumption of the driving meansfor the auxiliary mixing tool is large, thus permitting an accuratecomparison between the actual and required values, that is, be-

tween the actual and required consistency of the material.

Controlling the consistency of the material by auto-- matic moisteningof the material may be carried out with greater precision, and theapparatus required for that purpose is simplified.

The temperature of the material may, if desired, be taken intoconsideration at the same time. Normally used sand is employed in thepreparation of molding sand. The used sand stripped from castings mustbe processed so that it has uniform qualitative properties when utilizedin the mixing container. In addition to its residual moisture content,the temperature of the used sand varies within wide limits and must becooled to a predetermined starting temperature for the proper automatedmixing of the molding sand. The temperature of the sand is carefullychecked prior to its introduction into the mixing container and then,based on its temperature, a control device admits the requisite amountof water into the sand so that its temperature can be brought to thedesired level by evaporation.

Depending on the consistency of the material,which can for examplecomprise moulding sand, ceramic material, concrete, lime sandstonematerials, granulated materials, and pressing and ramming materials, theresistance to mixing and the power consumption may be in widelydifferent ranges. It is therefore advantageous for the driving means forthe auxiliary mixing tool to be a variable speed electric motor,preferably a polechanging motor. In this way, depending on theconsistency of the material or the nature of individual components ofthe material, the most favorable treatment for each particular case canbe achieved.

Finally, care should be taken that the moisture introduced into themixing material to achieve a predetermined consistency does not exceedits desired value unless additional apparatus is provided for removingmoisture. It is therefore important that the moisture be distributedrapidly in the material; as otherwise, under certain circumstances, anexcessively lower power consumption may momentarily be indicated and anincorrect control order be transmitted to the regulating apparatus,resulting in the further excessive addition of moisture. A regulatingsignal corresponding to the power consumption of the motor mustpreferably therefore be derived when almost unvarying conditions areobtaining in the apparatus, that is, in particular, when the tool isrotating at a speed which is uniform and therefore free fromacceleration, and the material is sufficiently homogenised forcontinuation of the mixing operation not to vary the power consumptionof the motor.

In order to ensure that the further addition of moisture is only derivedfrom the power consumption signal after a substantially unvaryingcondition of the abovementioned nature has been achieved, the apparatusfor carrying out a two-stage method in which a given amount of moistureis firstly introduced into the material and, subsequently, furthermoistening is controlled in dependence on the power consumption of themotor, can with advantage be embodied with a regulating apparatus whichhas an adjustable time delay operable after the first supply ofmoisture. This time delay can be made correspondingly larger when thetime constants in the control circuit affect the measurement, so thatthe measured values of the power consumption are in fact taken asconsistency values measured in the substantially unvarying condition ofthe material, and are transmitted to the regulating apparatus for thepurposes of further controlling the moistening operation.

BRIEF DESCRIPTION OF TI-IE DRAWINGS Two embodiments in accordance withthe invention will now be described by way of example with reference tothe'accompanying drawings, in which:

FIG. 1 shows the first embodiment in diagrammatic form; i

FIG; 2'shows the second embodiment in block form;

FIGS. 3 to show the electric circuit of the second embodiment, thecircuit being. completed by placing FIG. 4 to the right of FIG. 3, andFIG. 5 to the right of FIG. 4; and

FIGS. 6 and 7 show the control diagram for a control device forregulating the temperature of the materials changed into the secondembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, acounter-flow mixer comprises a clockwise-rotating mixing container 2 inwhich operates a relatively low-speed anti-clockwise-rotating mainmixing toolA having a plurality of mixing blades, and a high-speedlow-inertia auxiliary mixing tool B. The container 2 is rotated by agear motor 2a which drives a ring gear 2b secured to the container; Theaxes of rotation of both tools A and B are eccentric relative to theaxis of rotation of the container 2, and the tool B lies outside theworking area of the'tool A.

In operation, a known amount lof material to be mixed and moistened isput into the container 2 and treated with an amount-3 of fluid.Hereinafter the material will be assumed to be casting sand and thefluid water. In a first mixing stage, which is not necessarilyregulated, the amount of water is metered by a meter 14 controlling avalve in such a way that, together with the usual initial water contentof the sand, the sand is still definitely below the desired final watercontent necessary to achieve the desired consistency or plasticity. Thisfirst stage prepares for the subsequent stage of finely regulating thewater content, and also brings the water content to a value at which theelectric current or power used by an electric motor 4 driving the tool Bcan be satisfactorily measured.

The sand is then homogenised by the tools A and B, during which stepmany materials have a tendency to increase in volume up to an expansionlevel 6. For clarity, the levels 3 and 6 are shown in exaggerated form.Further high-speed tools, combined with stationary tool systems. canalso be used instead of the tools A and B. The uniform distribution ofthe .water can be achieved in a short period of, for example, l() toseconds, after which time a magnetic valve 7 controlled by a time relay13 opens, so that valves 8a to 8d are acted upon by water pressure.

The power used by the motor 4 in driving the tool B is then measured bya power measuring means having contacts 10a to 10d. There is normallyconnected be tween the motor 4 and the power measuring means a measuredvalue treatment unit 11 by means of which the measured value istransformed and smoothed. When the sand is homogeneous the power used bythe motor 4 is a direct, generally non-linear, function of theconsistency of the sand. As the motor 4 is driven by a constant networkvoltage, the reading of the power measuring means is proportional to thecurrent used and causes one or more of the contacts 10a to 10d to betripped so that the measured value which is obtained in analog form isquantised in four steps. Depending on the number of contacts 10a to 10dtripped, a control unit 12 acts on the magnetic valves 8a to 8d in sucha way that any of the contacts 10a to 10d tripped cause thecorresponding valves 8a to 8d to be opened.

The amount of water allowed into the sand during this second stagedepends on the condition of the valves 8a to 8d, the common supply pipe16 to which a is throttled after a predetermined period by the magneticvalve 7. In this way, the amount of water added depends on the number ofvalves 8a to 8d open, and this is determined by the consistency of thesand following the firststage. Following the addition of the water inthe second stage the sand is again homogenised and subsequentlydischarged. All the control and regulating elements are then returned totheir initial conditions.

The above described method and the apparatus can be modified in variousways without going outside the scope of the invention. Thus the valves8a to 8d could be closed by flow measuring means instead of the timerelay 13. Depending on the specific use to which the apparatus is put,the valves 8a to 8d can also be formed as regulating valves, regulatingcocks, snap valves or restrietor valves with a large flow cross-sectionif thick or viscous fluids are used for moistening. The valve controlcan be effected by potentiometers which fully open the valves initiallyand then successively close them in dependence on the power used by themotor If the motor 4 is a three-phase motor, the abovementioned powermeasuring means will desirably be used, while with a direct-currentmotor a contact ammeter is preferable. When hydraulic motors are used todrive the tools A and B, they are combined with known regulating andmeasuring devices.

The invention permits reliable control of the moistening operation andrapid homogenisation of the sand. By using a constant weight of said,supplied from a charging container 2A, a high degree of measuringprecision can be achieved because of the possibility of reproducing thevalues of power used relative to a given water content, and hencecalibrating the power measuring means. Also, a high-speed low-inertiaauxiliary tool has a sensitive reaction to variations in water contentof the sand, so that the range of power used is extended anddifferentiation between different water contents increased; Thesensitivity and precision of the regulation is still further increasedif the motor 4 is connectcd directly, that is without the interpolationof gears, to the tool B. Additionally, it has been found advantageous ifthe motor 4 maintains its speed of rotation substantially constantwithin the measuring range. As different measuring ranges are founddesirable for different materials, it is of advantage for the motor 4 tobe pole-changing.

It has been found preferably for the tool B to be in the form of aH-shaped spinner 5, the bars of which diverge upwardly in a V-shape.However other tools suited to the specific properties of the materialcan also be used.

In the apparatus shown in FIGS. 2 to 5, two limit contacts areassociated with the power measuring means W coupled to the motor 4 forthe auxiliary tool B. With the two limit contacts in this embodiment, afour-stage mode of operation is achieved by means of a suitable circuitconnected to the power measuring means W and in this way the requiredwater content can be approached in steps.

In order to make the cycle time of the mixer as short as possible, theapparatus should be set very rapidly and automatically to the watercontent which is still missing from the material. The amount of water inthe old sand which is found for example in foundries, can however varywithin wide limits. If for example the water content in the sand whichhas not yet been treated is in the vicinity of the required value, thefirst stage, which generally adds a large amount of water, and possiblyeven the second stage, are omitted so that then only the third andfourth stages are operative, with correspondingly'smaller amounts ofwater added. The sequence in time of the additions of water and theamounts of water to be added can therefore be adjusted as desired aswill now be described.

In HO. 2, the container 2 is shown diagrammatically with a main mixingtool A and a spinner or auxiliary tool B, the motor 4 of which iscoupled to the power measuring means W. The power measuring means Wtransmits a signal to a pulse transmitted U1 which actuates the countingcircuit Z. The counting circuit Z is connected to a transmitter U3 whichactuates a magnetic valve V for the required water supply periods andintervals.

The magnetic valve V can be actuated in four modes by the transmitter U3in the embodiment shown, the variation in the supply periods andintervals in each mode resulting in a variation in the amount of wateradded. With the shortest supply period and the longest interval, thethrough-put is 0.25 litres per minute, whilst with the longest supplyperiod and the shortest interval, the throughput is 60 litres perminute.

The mode of operation of the metering control circuit with four-stageautomatic operation will now be described with reference to FlGS. 3 to5. The metering operation is initiated when a switch B1 in the currentpath 12 is temporarily closed. This results in the relay dlA beingenergised, whereby the contacts DlA in the current path 39 are closed.This results in the control voltage for the metering apparatus beingconnected.

The relay d3 in the counting circuit Z is engaged by way of the restcontacts D2/O in the current path 18. The relay d3 closes inter alia thecontact D3 in the current path 24 which supplies voltage to twopotentiometers (not shown) of the transmitter U3, which serve to adjustthe water supply period and interval of the first mixing stage. Thesetwo potentiometers are built into the transmitter U3 together with theinterval potentiometers of the second, third and fourth mixing stages.Therefore, for each stage there is provided a potentiometer foradjusting the supply period of the valve V and a potentiometer foradjusting the interval. The transmitter U3 therefore acts as a pulsetransmitter with variable supply periods and intervals. The intervalsmust be selected in such a way that the water which is added during thefirst supply period of the magnetic valve V mixes thoroughly with thesand. Only then does the power measuring means W indicate a rise inpower consumption by the motor 4, and only after the power rise hasterminated should the second addi tion of water take place.

Owing to the relay d3 being energised, the contact D3" in the currentpath 35 is also closed, energising the relay d12. As a result, the restcontact D12 in the current path 43 is opened, which opens the circuit ofthe voltage path for the power measuring means W, which path includesthe resistor R1. At the same time the working contact D12 in the currentpath 43 is closed, which closes the voltage path by way of the variableresistor R3 and the resistor R2. A voltage varied for example by 20percent can be delivered to the power measuring means W by the resistorR3. By means of such an increase in voltage in the voltage path, theindication of the indicator (not shown) of the power measuring means Wcan be made to exceed the actual power consumption of the motor 4.

As already mentioned, the closed contact D3 in the current path 24passes voltage to the two potentiometers for the first stage and by thecontact u3 of the transmitter U3, the valve relay d9 in the current path28 is energised and de-energised according to the supply periods andintervals set in the two potentiometers. Accordingly, the supply ofwater to the sand is effected by the valve V. For this purpose, thevalve relay d9 switches the contacts D9 in the current path 11 whichincludes the valve V.

Only after a certain interval does the sand react to this addition ofwater and put up a higher mechanical resistance to the tool B. Thiscauses an increased power consumption by the motor 4 and the indicatorof the power measuring means W leaves the minimum mark, whereupon therelay dl4 in the current path 41 is energised. The contact D14 in thecurrent path 31, which is supplied with voltage by way of the closedcontacts D15 of the relay dlS, energises the relay dll in by way of thecontact D3 which is also closed by the relay dll. The rest contact D11in the current path 28 then opens and de-energises the valve relay 9.The working contact D11 in the current path 16 is closed at the sametime by the relay dll and transmits voltage to the terminal 5 of thetransmitter U1.

The transmitter U1 is also a pulse transmitter with variable workingperiods and interval. The working period of the pulse transmitter Ul isset to be very short as it acts to restrict the transmission of pulses,while the interval period acts as a response delay, so that theindicator of the power measuring means W is generally not quite at restin operation of the metering apparatus, and so that its first maximumdeflection should not initiateany stepping of the counting circuit Z. Inother words, the supply of water to the sand should be stopped at thatmoment, but the pulse transmitter U1 should not yet step the countingcircuit Z on to the next stage.

When the indicator of the power measuring means W has finally moved offthe minimum mark, the contact ul of the transmitter U1, which contact ullies in the current path 14, closes temporarily, and the coil 42 of thecounting circuit Z which also lies in the current path 14 is energised.As a result, the counting circuit Z is stepped on by one step. Theresult of this is that the rest contact D2/O opens and the workingcontact D2/ 1 in the current path 19'closes. The contact D2/1 energisesthe relay d4 in the current path 19, of which the working contact D4which is in the current path 25 then closes and transmits voltage to thetwo potentiometers for the supply periods and intervals of the secondstage. The transmitter U3 energises and de-energises the valve relay d9according to the values set by way of the contact u3, and the watersupply of the second stage takes place.

Owing to the relay d3 becoming de-energised, the relay dl2 is alsode-energised by way of the contact D3", the contacts D12 and D12 of therelay dl2, which lie in the current path 43, switching the voltage pathof the power measuring means W to normal voltage. As a result of thisswitch to normal voltage, the indicator of the power measuring means Wreturns to the minimum mark and the relay dl4 becomes deenergiscd, thecontact D14 opening. At the same time the contact D3 in the currentpath31 opens and deenergises the relay dll. The rest contact D11 of therelay d1 1 which lies in the current path 28 prepares for the energisingof the valve relay d9. The working contact D11 of the relay d3simultaneously interrupts the control voltage for. the transmitter U1 sothat further stepping on of the counting circuit Z is prevented.

At this moment, the power measuring means W is operating withoutincreased voltage. If now the power consumption of the motor 4 is againincreased by the supply of water in the second stage, the indicator ofthe power measuring means W again moves off the minimum mark. The relaydl4 is again'energised and its working contact D14, which is in thecurrent path 31, energises the relay dll by way of the contact D4 in thecurrent path 32, which contact has already been closed by the relay d4.The rest contact D11 of the relay d1] de-energises the valve relay d9.The working contact D11 is closed at the same time and transmits controlvoltage to the transmitter U1. The transmitter Ul steps the countingcircuit Z by a further step, as already described above.

In that case, the relay d4 becomes de-energised and the relay d of thecounting circuit Z'is energised by way of the closed contact D2/2. Thecontact D4 in the current path 32 opens owing to the relay d4 becomingde-energised and de-energises the relay d1 1. The work ing contact D5 isclosed by the relay d5 and transmits voltage to the two potentiometersin the transmitter U3 for the supply periods and intervals of the thirdstage. At the same time, the working contact D5 in the current path 36is closed and transmits voltage to the relay d13 in the same currentpath. The relay d13 actuates the switching contact D13 and D13 in thecurrent path 44, which interrupts the voltage path of the powermeasuring means W by way of the resistor R1 and switches the latter tothe variable resistor R5. Depending on the particular setting of thelatter, an increased voltage is then again transmitted to the voltagepath of the power measuring means W, which results in an increased powerconsumption indication. From this it is apparent that the voltageincrease in the first and third stages can be adjusted separately.

The valve relay d9 which actuates the valve V is energised andde-energised, as already mentioned, by the transmitter U3. When theindicator of the power measuring means W finally reaches the maximummark, the relay d15 in the current path 42 becomes deenergised. The restcontact D 15 of the relay d15, which lies in the current path 33, closesand energises the relay d1 1 by way of the working contact D5 which isalready closed. The relay dll tie-energises the valve relay d9 by way ofthe contact D11 and supplies voltage to the transmitter U1 by way of thecontact D11, as already described above. As a result, the countingcircuit Z is stepped on by one step. The relay d5 of the countingcircuit becomes de-energised and the relay d6 becomes energised byvirtue of the contact D2/3 being closed. Owing to the de-energisation ofthe relay d5, the relay 13 inthe current path 36 is de-energised by wayof the contact D5 Also, the switching contact D13, D13 which lies in thecurrent path 44 and which is actuated by the relay d13 switches thevoltage path of the power measuring means W back to normal voltage. Thiscondition is shown in FIG. 5. The result of this is that the indicatorof the power measuring means W again moves off the maximum mark so thatthe relay dl5' is again energised.

The two potentiometers in the transmitter U3 for the supply periods andintervals of the fourth and last stage are energised by the relay d6.The transmitter U3 again accordingly actuates the valve relay d9. Thisresults in a further supply of water to the sand and the indicator ofthe. power measuring means W again returns to the maximum mark, owing tothe rising power consumption of the motor 4. As a result, the relay dlSis again de-energised and its rest contact D15 which is in the voltagepath 33 energises the relay d11 by way of the working contact D6 in thecurrent path 34, which contact is already closed by the relay d6. Therelay d11 de-energises the valve relay d9 and transmits voltage to thetransmitter U1 by way of the contact D11. The transmitter U1 thereuponsteps the counting circuit Z by a further step. The working contact D2/4of the counting circuit 2, which contact lies in the current path 22,transmits control voltage to the terminal 5 of the reset circuit U2 forresetting the counting circuit Z. The working contact u2 of the circuitU2 which lies in the current path 13, energises the coil dlZ, wherebythe control voltage for the entire apparatus is interrupted by way ofthe contact dlZ in current path 37. The'working contact u2 of the resetcircuit U2, which contact lies in the current path 15, transmits ahalfwave rectified voltage by way of the zero-position contact D2 to thecoil 42 which thereupon returns the counting circuit Z to its zeroposition. The pulse transmission of the reset circuit U2 lasts for about1 second.

After the above switching operation has taken place, the supply of wateris concluded and the apparatus is ready for a new metering operation.

If, by virtue of the power measurement, it turns out that there isinitially a relatively large amount of water in the sand, the variousstages are omitted until the power measuring means W indicates a valuewhich shows that the addition of water is necessary. Manual release ofthe valve relay d9 for corresponding switching of the magnetic valve Vis also possible by way of the manual switches B3 and B4 in the currentpath 30.

Instead of the above described circuit with a power measuring means W,the principle upon which the invention is based can also be embodied bya control circuit having for example a current measuring means with anelectronic coefficient forming means, or any other measuring device forsupplying the necessary measured values.

If materials having widely varying starting temperatures are to beprocessed, additional temperature sensors 50 are employed in combinationwith a control device 52 to correct the influence of temperature on theamount of water contained in the material. The control device 52 isconnected to the control unit 12.

in preparing the materials to be mixed, the mixing container 2 mustbecharged with uniform size batches. A material supply hopper 54 ispositioned above the mixing container 2 for introducing the uniform sizebatches into the container. The temperature sensing means SOarelocatedwithin the hopper 54 at several positions so that a reliable mean valueof the temperature of the material, such as used foundry casting sand,to be introduced into the mixing container is obtained. The temperatureof used sand can fluctuate from normal room temperature, approximately20C to or above 100C. For example, at the outset of a work week, afterthe weekend shutdown, the use casting sand is available at roomtemperature, however, during the work week the sand is hot if it isstripped from the molds as quickly as possible following the castingoperation. if the temperature differences of the starting material isnot taken into consideration it is not possible to automate the mixingprocess because the material at the commencement of mixing will not beat the re quired temperature for obtaining the needed consistency inprocessing each batch of material.

in FIGS. 6 and 7 the control diagram of the control device 52 is shownfor dissipating any excess heat contained in the casting sand.

In FIGS. 6 and 7 a plug panel U21, U22 is divided into temperatureranges of intervals from 5 to 100C. To cool the casting sand to therequired starting temperature for the mixing operation, water isintroduced into the sand and the temperature is reduced by evaporation.The amount of water added is based on the temperature of the startingmaterial in the supply hopper 54. To determine the amount of waterneeded to cool the sand, tests are run before the mixing container isplaced in operation and the plugs are arranged in the panel tocorrespond to the amount of water required for each temperature rangerecorded. Along the upper edge of the plug panel U21 numbers 1, 2, 4, 8,10, 20, 40 and 80 appear indicating liters. The size and gradations ofthe plug panel naturally depend on the size of the mixing containerinvolved and the amount of water supplied also depends on the container.

As mentioned above, the dissipation of excess heat is attained basicallythrough evaporation and the cooling time required for each batch ofmaterial introduced into the container depends upon the quantity ofwater to be evaporated. Another plug panel U2 1a establishes the coolingperiod exactly. The vertical coordinate of the plug panel U2la isdivided into a temperature range from 45 to 95C and the horizontalcoordinate has a scale ranging from 10 seconds to 100 seconds. The sizeof the plug panel U2la depends of course, upon the size of the mixingcontainer and the operating conditions involved. The required coolingperiods is determined by preliminary testing and is set forth in atable. The plugs are arranged in the panel before operation iscommenced. Corrections necessitated by seasonal variations in theambient temperature, can be made at any time by repositioning the plugs.

In providing the material at the proper starting temperature the aboveapparatus is operated as follows:

The temperature sensors within the supply hopper 54 determine thetemperature of the charge of material to be placed into the mixingcontainer 2 and the sensors exert joint influence upon a counting'relay(decimal counter) associated with the plug panels. At the same time, thetemperature of the material may be read optically. The counting relay isalso provided with an optical indicator so that the sand temperature canbe checked to ascertain the correctness of the temperature readings.

Alongside the plug panels U21, U22 a row of counting relays is arrangedcorresponding to the gradation of the temperature scale. F or instance,if the temperature sensors indicate the temperature of the material tobe 80C, the relay U12, contact 16, responds and through its connectionto the plug panel U22 determines the amount of water to be added.Further, the relay U12, contact 16, also establishes the cooling periodto be used in accordance with the values arranged in the plug panelU2la.

The plug panels U21, U22 have a binary layout, that is, the decade hasonly four members, i.e. l, 2, 4 and 8, which can be used in making anydesired addition of cooling water. The cooling period is divided indecimals so that each plugged-in value corresponds to the tabulatedcooling period.

With the temperature of the material to be added having been determined,the material is directed automatically from the supply hopper 54 intothe mixing chamber 2 and a dry mixing period is commenced. The drymixing period is infinitely variable and generally amounts to only a fewseconds. .When the dry mixing period is completed, the control device 52feeds the required amount of water into the container for cooling thematerial to be mixed. As the water is added a wet mixing period takesplace which is also infinitely variable and during the wet mixing periodthe actual homogenisation of the material takes place. Concurrently withor immediately following the end of the wet mixing period the coolingperiod, determined from the plug panel U2la is effected. During thecooling period, a strong air current is directed through the mixingcontainer 2 from pressure and suction blowers 56. Normally, the blowersare in continuous operation. The start and end of the cooling period iscontrolled by opening and closing the suction side of the blowers.

At the completion of the cooling period, the material in the containeris at the desired temperature and isthoroughly mixed. At this point thefine adjustment of the consistency of the material can be effectedthrough the consumption of energy by the mixing tool B. There is noexcess water in the material, since it has been evaporated during theprior cooling period. Accordingly, the mixing operation, as describedabove, is performed so that the material is in the proper consistencyfor use in carrying out the casting operations.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the inventiveprinciples, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:

1. Apparatus for moistening a mixable material by the multi-stageaddition of a moistening liquid, comprising a container rotatable abouta substantially vertical axis and arranged to hold the material to bemixed and moistened, a vertically arranged relatively lowspeed rotatablemain mixing tool located within said container for mixing the material,a vertically arranged high-speed low-inertia auxiliary mixing toollocated within said container and spaced laterally from said mixing toolso that its path of rotation is outside the path of rotation of saidmain mixing tool, driving means for rotating said auxiliary tool in thematerial, means for a step-wise addition of moistening liquid to thematerial to bring its moisture content to a predetermined level, controlmeans for regulating said means'for a step-wise addition of moisteningliquid to the material determined in dependence on the power consumptionof said driving means for said auxiliary mixing tool, and said controlmeans includes a means for affording an interval in which. themoistening liquid thoroughly .mixes with the material before the powerconsumption of said driving means is determined, wherein the improvementcomprises a hopper for supplying measured quantities of material intosaid container, temperature sensing means positioned within said hopperfor determining the temperature of the material to be supplied into saidcontainer, and said control means includes a control device connected tosaid temperature sensing means for regulating the admission of coolingwater to said container and regulating the cooling period after theadmission of the water based upon the temperature determined by saidtemperature sensing means for establishing a predetermined startingtemperature for the material within said container prior to themulti-stage addition of the moistening liquid.

2. Apparatus, as set forth in claim 1, wherein said control deviceincludes a plug panel arranged to regulate the amount of water to beadded to the material in said container in accordance with thetemperature determined by said temperature sensing means, and anotherplug panel arranged to regulate the time duration of the cooling periodbased on the temperature of the material as determined by saidtemperature sensing means. I

3. Apparatus, as set forth in claim 2, wherein blowers are associatedwith said container for providing a flow of air through said containerduring the cooling period. l=

1. Apparatus for moistening a mixable material by the multistageaddition of a moistening liquid, comprising a container rotatable abouta substantially vertical axis and arranged to hold the material to bemixed and moistened, a vertically arranged relatively low-speedrotatable main mixing tool located within said container for mixing thematerial, a vertically arranged high-speed low-inertia auxiliary mixingtool located within said container and spaced laterally from said mixingtool so that its path of rotation is outside the path of rotation ofsaid main mixing tool, driving means for rotating said auxiliary tool inthe material, means for a step-wise addition of moistening liquid to thematerial to bring its moisture content to a predetermined level, controlmeans for regulating said means for a step-wise addition of moisteningliquid to the material determined in dependence on the power consumptionof said driving means for said auxiliary mixing tool, and said controlmeans includes a means for affording an interval in which the moisteningliquid thoroughly mixes with the material before the power consumptionof said driving means is determined, wherein the improvement comprises ahopper for supplying measured quantities of material into saidcontainer, temperature sensing means positioned within said hopper fordetermining the temperature of the material to be supplied into saidcontainer, and said control means includes a control device connected tosaid temperature sensing means for regulating the admission of coolingwater to said container and regulating the cooling period after theadmission of the water based upon the temperature determined by saidtemperature sensing means for establishing a predetermined startingtemperature for the material within said container prior to themulti-stage addition of the moistening liquid.
 2. Apparatus, as setforth in claim 1, wherein said control device includes a plug panelarranged to regulate the amount of water to be added to the material insaid container in accordance with the temperature determined by saidtemperature sensing means, and another plug panel arranged to regulatethe time duration of the cooling period based on the temperature of thematerial as determined by said temperature sensing means.
 3. Apparatus,as set forth in claim 2, wherein blowers are associated with saidcontainer for providing a flow of air through said container during thecooling period.